As the use of wireless technology has grown, there has been an increase in the amount of data that is being used by wireless devices, which must be transferred over the wireless networks. Also the traffic comprises many different types, each with a unique Quality-of-Service (QoS) requirements that should be met by the network. To accommodate this increase in traffic and the variation in QoS requirements, data streams are generally split up into discreet data packets, which are then transmitted from the transmitter to the receiver. The receiver may treat data packets of one stream differently from other streams to achieve the required QoS requirements for that stream. Once received, the receiver can then take these individual data packets and use them as desired.
However, due to impairments that may arise in the channel during transmission, wireless links may utilize a protocol in order to ensure that individual data packets are not simply lost during transmission. One type of protocol is an Automatic Repeat ReQuest (ARQ) protocol to ensures that data is transmitted reliably between a transmitter and a receiver, such as between a base station and a mobile station. In ARQ protocols the transmitter transmits a coded or uncoded data bits in a frame, or parts of the frame, as many times as required for the receiver to correctly receive the uncoded data bits. A frame refers to bits, which is delimited with a clear start and an end. In upper layers, the frame is also referred to as a packet. In lower layers, the frame is also referred to as a transport block (TB).
ARQ protocols can be classified into pure ARQ protocols and hybrid ARQ (HARQ) protocols. Pure ARQ protocols rely on lower level protocols to provide protection against bit errors, while HARQ protocols use forward error correction (FEC) to provide bit-level error protection. ARQ protocols include Stop-and-Wait, Go-back-N and Selective-Repeat protocols. ARQ protocols use sequence numbers, parity checks on sequence numbers, acknowledgment timers, and state machines to detect packet and acknowledgement losses. The general idea of ARQ protocols is that the packet sender keeps retransmitting a packet or packets until it receives the correct acknowledgment(s). The receiver acknowledges packets with an acknowledgment signal. The approach of retransmitting a packet until it is acknowledged may potentially result in a very high number of retransmissions and thus high latency in ARQ protocols.
Unlike ARQ protocols, where each frame's retransmission is treated independently of other frame transmissions of the same frame, in HARQ protocols, the receiver decodes received copies of the frame, or partial copies of the frame, jointly using soft combining. The receiver uses all received coded bits to recover the original data.
However, previous uses of ARQ/HARQ protocols have serious limitations, and may not be able to handle the more stringent requirements that are utilized for greater transmission speeds, higher data loads, and wider range of QoS differentiation than was experienced in previous wireless traffic.